It is known to use X-ray sources to obtain computerized tomography images. In many prior art applications (and particularly in the field of medical applications) the object being scanned lies fully within the X-ray source fan angle. There are situations, however, when computerized tomography images for relatively larger objects are desired (for objects such as, but not limited to, automobiles and/or larger automobile components, rocket motors, cargo containers, and so forth); i.e., objects that are larger than the available X-ray source fan angle. Also in many prior art applications, the object (such as a human body) comprises a relatively soft or less opaque object, thus requiring smaller amounts of X-ray energy to obtain useful images. There are again situations, however, when computerized tomography images for relatively larger, harder, more opaque objects are desired (again for objects such as, but not limited to, automobiles and their components, rocket motors, cargo containers, and so forth). Considerably higher amounts of X-ray energy are typically required to obtain useful images with such objects.
The challenges become particularly acute when these two problems coincide; that is, when a relatively large object also comprises a relatively opaque object. It becomes quickly impractical (economically and/or physically) to provide a large enough X-ray source to provide both sufficient power and a sufficiently large X-ray source fan angle to accommodate such objects. By one prior art approach, larger objects are scanned using translate/rotate geometries in conjunction with high energy X-ray sources. Such systems often employ detector designs having relatively small apertures as compared to their corresponding detector pitch (often known as small aperture/large pitch detectors) in order to attempt to provide high spatial resolution and good image quality. Unfortunately, such an approach occasions numerous problems including, but not limited to, large and complex mechanical configurations, alignment and accuracy challenges, relatively slow scanning speed, difficulty with or an inability to scan an object in an optimum position for that object, and non-flow through system operation to name a few.
Rotate only geometries have also been proposed (particularly for tangential scanning modes when scanning rocket motors). This approach fails to provide accurate whole object images and typically only accommodates circularly symmetrical objects. Also, this approach only provides accurate images of circumferential details in the outer annulus of the object; radial details and inner ring details are incorrectly imaged.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the arts will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.